Skin aging is commonly viewed as wrinkle formation and impaired wound healing. A wound is defined as a break in the epithelial integrity of the skin. Normal wound healing involves a complex and dynamic but superbly orchestrated series of events leading to the repair of injured tissues. The largest component of normal skin is the extracellular matrix (ECM), a gel-like matrix produced by the cells that it surrounds. The ECM is composed of two major classes including fibrous structural proteins and proteoglycans. Changes in the composition and crosslinked state of the ECM are known to be associated with aging and a range of acquired and heritable skin disorders. It has been well documented that ECM not only provides structural support, but also influences cellular behavior such as differentiation and proliferation. Also, more and more research suggests that the matrix components may be a source of cell signals to facilitate epithelial cell proliferation and migration and thus enhance wound healing.
The largest class of fibrous ECM molecules is the collagen family, which includes at least 16 different types of collagen. Collagen in the dermal matrix is composed primarily of type I (80-85%) and type III (8-11%) collagens, both of which are fibrillar, or rod-shaped, collagens. The tensile strength of skin is due predominately to these fibrillar collagen molecules, which self-assemble into microfibrils in a head-to-tail and staggered side-to-side lateral arrangement. Collagen molecules become cross-linked to adjacent collagen molecules, creating additional strength and stability in collagen fibers. Damage to the collagen network (e.g. by enzymes or physical destruction), or its total collapse causes healing to take place by repair.
Various bioactive peptides that stimulate production of ECM proteins have been reported in both the scientific literature and in issued patents. Peptides historically have been isolated from natural sources and have recently been the subject of structure-function relationship studies. Natural peptides have also served as starting points for the design of synthetic peptide analogs.
Specific sequences within ECM proteins can stimulate useful elements in skin, such as type I collagen, type III collagen, and fibronectin (Katayama et. al., J. BIOL. CHEM. 288:9941-9944 (1983)). Katayama et al. identified the pentapeptide, KTTKS (SEQ ID NO:17), within the carboxy-terminal propeptide (residues 197-241) of type I collagen. The propeptide is cleaved during production of the mature collagen protein. The cleaved propeptide may participate in regulating collagen production via a biosynthesis feedback mechanism, with the KTTKS segment playing an active role. Maquart et al. (J SOC BIOL. 193:423-28 (1999)) reported that the peptides GHK and CNYYSNS also stimulate ECM synthesis. These sequences may be released during ECM turnover, thereby signaling the need for ECM repair. The short peptide sequences liberated by either mechanism are often called “matrikines” (Maquart et al., J. SOC. BIOL. 193:423-28 (1999)).
While a number of natural and synthetic peptides exist, there is a need for improved biologically active peptides and methods for their use.